1. Field of the Invention
The present invention relates to a stop determination device for determining whether or not an internal combustion engine is in a stop state.
2. Description of the Related Art
To date, internal-combustion-engine stop determination devices have been disclosed (e.g., refer to Japanese Patent Laid-Open No. 2001-263147) in which a rotation-direction detection unit for detecting the rotation direction of the crankshaft of an internal combustion engine is provided, and in the case where a backward rotation of the internal combustion engine is detected based on a signal from the rotation-direction detection unit, or in the case where the rotation speed of the internal combustion engine is lower than a reference value, it is determined that the internal combustion engine is in a stop state.
In a conventional internal-combustion-engine stop determination device disclosed in Japanese Patent Laid-Open No. 2001-263147, in the case where, upon a stop of an internal combustion engine, a backlash causes the crankshaft to rotate backward, a stop determination unit determines that the internal combustion engine has stopped; therefore, there exists no delay time that may occur with a stop determination method utilizing no rotation direction because that stop determination method cannot distinguish a signal upon a backward rotation due to a backlash from a signal upon a forward rotation, whereby it can rapidly be determined that the internal combustion engine has stopped, in response to an actual stop of the internal combustion engine.
Meanwhile, to date, internal combustion engines have been disclosed (e.g., refer to National Publication of International Patent Application No. 2003-515052) in which a combustion starting method is utilized in which a fuel is injected into a cylinder in a compression stroke and ignited so that the crank shaft is made to rotate backward and thereby the engine is started.
In the case of the internal-combustion-engine stop determination device disclosed in Japanese Patent Laid-Open No. 2001-263147, the usage mode and characteristics of a crank angle sensor that detects the rotation direction of a crankshaft causes the following anxieties: In the first place, a case will be considered in which, as illustrated in FIGS. 13A and 13B, while a detection subject 4 is situated in the vicinity of the detection coverage of a crank angle sensor 2, a backlash at the time when the internal combustion engine stops, a vibration at the time when the internal combustion engine is in a stop state, or the like causes the states of FIGS. 13A and 13B to be alternately repeated. In this case, the crank angle sensor 2, which does not detect the rotation direction of the crankshaft, cannot be utilized in a state in which the engine may rotate backward, for example, immediately before a stop of the engine; therefore, the conventional internal-combustion-engine stop determination device is configured in such a way that the detection subject 4 is not detected when the engine rotates at extremely low speed or in such a way that the crank angle sensor 2 is prohibited from outputting a signal. Accordingly, even in the case where the states of FIGS. 13A and 13B are alternately repeated, no signal is outputted, whereby a stop determination of an internal combustion engine can rapidly be performed, and even in the case where the foregoing case is caused by a vibration or the like after the internal combustion engine has stopped, the stop determination is continued and thereby no problem is caused.
However, in the case of the crank angle sensor 2 that detects the rotation direction of an internal combustion engine, especially, the crank angle sensor 2 for the purpose of detecting a stop position, the position of the detection subject 4 has to be accurately detected by a time instant when the engine stops, and also when the rotation direction reverses, the rotation speed temporarily becomes “0”; therefore, even in a stop state, the crank angle sensor 2 is required to output a signal. Accordingly, also when the states of FIGS. 13A and 13B are alternately repeated, a forward-rotation signal and a backward-rotation signal are alternately outputted; thus, with a conventional stop determination device, the stop determination is cancelled by the forward-rotation signal. As a result, the stop determination may be delayed, or the conventional stop determination device may erroneously determine that the internal combustion engine has restarted, whereby unnecessary starting control may be activated. Also when the foregoing state is caused by a vibration or the like after the internal combustion engine has stopped, the stop determination may be cancelled and thereby the conventional stop determination device may erroneously determine that the internal combustion engine has started.
In contrast, in the case of an internal combustion engine, disclosed in National Publication of International Patent Application No. 2003-515052, which employs a so-called combustion starting method in which a fuel is injected into a cylinder in a compression stroke and ignited so that the crank shaft is made to rotate backward and thereby the engine is started, the conventional stop determination device disclosed in Japanese Patent Laid-Open No. 2001-263147 may erroneously determine a state of reversal or a state of extremely low speed rotation as a state of stop, even though the internal combustion engine has been activated; thus, activation of internal-combustion-engine starting control may be delayed.